Radio receiver



Dec. 10, 1940. w. J. SCHNELL RADIO RECEIVER Original Filed May 21, 1958ATTORNEY-9.

Patented Dec. 10, 1940 UNITED STATES PATENT orrlcs RADIO RECEIVERWilliam J. Schnell, Berwyn, Ill., assignor to Electrical ResearchLaboratories Inc., Chicago, 111.,

a corporation of Illinois 5 Claims.

This invention relates to a radio receiver and more particularly to avolume control circuit for the receiver.

It is an object of this invention to provide means for controlling thevolume of a radio receiver from a truly remote point.

The well known Bowden cables for mechanically operating the volumecontrol resistor of a radio receiver are of course unsatisfactory for 10any substantial distance or for home use. It has heretofore beenproposed to control the volume of the receiver from a remote point butsuch electrically operable remote volume control devices as have beensuggested have been either com- 15 plex in character or unsatisfactorybecause of the inherent capacity existing between the wire leads to theremote point, which inherent capacity has heretofore produced distortionor howling in the sound reproduction circuits of the re- 20 ceiver.

It is therefore a further object of applicants invention to provide asimple, inexpensive and highly efiicient electrically operable remotevolume control preferably capable of energization 25 or energized by thealternating current supplied to the radio receiver.

Other and further objects and advantages of the invention will beapparent from the following description when taken in connection with 30the accompanying drawing showing a schematic diagram of a remote volumecontrol constructed in accordance with the invention.

The present application is a division of the application filed byWilliamJ. Schnell and Eugene 35 W. Masters, as Serial No. 209,170, filed May21.

A volume control circuit constructed in accordance with the principlesof the invention is schematically shown in the drawing. A thermionicvacuum tube 2, having a plate 4, a screen grid 8, an injector grid 8, acontrol grid i0, and a cathode l2, may constitute the first stage ofaudio-amplification of the radio receiver. The injector grid 8 isconnected through a condenser 45 14 to the coupling and volume controlresistor 35. The resistor l5, together with a condenser #0, couples theinput of the tube 2 to the output resistor 18 of a diode rectifier ordetector 20. The signal currents are supplied to the diode 20 50 bymeans of the secondary winding 22 of an interstage transformerconnecting the radio frequency or intermediate frequency amplifier tothe detector. Plate current is supplied to the tube 2 from the powersupply terminal 24 55 through the resistor 26 and the interstagecoupling condenser 28 connects the signal output of the tube 2 to theinput of the next succeeding stage of amplification. The screen grid 6is connected to the usual and suitable source of positive potentialrepresented by the terminal 30, a resistor 32 being connected in seriesin the screen grid lead 34 and a shunting condenser 36 being connectedto the lead 34 and to ground.

The cathode l2 may be heated in any desired and customary manner and maybe grounded as at 33 or otherwise connected to the free end of thecoupling and volume control resistor I5. The control grid I0 isconnected to the injector grid 3 through a resistor 40 and bias cell orsource 42 having its negative terminal connected to the injector gridand its positive terminal connected to the resistor 40.

A volume control resistor 44 is mounted at a remote point or station 45.One end of the remote volume control resistor 44 is connected by a leador wire 48 of a cable 50 extending between the remote station 46 and theradio receiver. At the radio receiver the wire 48 is connected to oneend of a secondary winding 52 of the power supply transformer, the otherside of this secondary being preferably grounded as at 54. The voltagesupplied by this secondary is preferably of the order of twenty-fourvolts. The other wire 50 of the cable 50 connects the adjustable tap 58of the volume control resistor 54 to the cathode of a diode rectifier60'. The plate of this diode rectifier is connected to ground at 02through a resistor 04. At the remote station the wire 5% and theadjustable tap 53 are connected to ground through a resistorlih. Afilter 68, comprising a resistor l0 and shunting condensers l2 and 14,connects the diode rectifier 60 to the control grid ill of the amplifiertube 2.

The operation of this circuit is substantially as follows. The'signalinput rectified by the diode 20 is impressed on the injector grid 8 ofthe tube 2 and the value of this voltage is controlled by the volumecontrol resistor l5 which is located in the receiver and is operated bythe knob on the front of the receiver. The remote volume controlresistor 44 determines the value of the alternating current voltageimpressed by the resistor $6 on the input of the diode rectifier 60 andin turn determines the value of the direct current bias voltageimpressed by the resistor 64' on the control grid It of the tube 2. Thefilter 68 filters the voltage impressed on the control grid. It will beapparent that by decreasing the value of the alternating current voltageacross the resistor 66, the resistance 44 being increased,

the direct current voltage or negative bias potential impressed by theresistor 64 on the control grid I and the injector grid 8 will becorrespo-ndingly decreased to thereby effect a decrease 5 in the bias ofthe grids and a consequent increase in the amplification power of thetube 2. The output signal volume of the tube 2 will therefore beincreased. An increase in the alternating current voltage across theresistor 66 will correspondingly effect a decrease in the volume of theoutput signal of the tube 2.

If desired, the input signal may be impressed on the control grid andthe injector grid used primarily for remote volume control purposes bymerely connecting the injector grid 8 to the point 16 and the controlgrid I 0 to the point 18.

It will be seen from the description of the drawing that the inventioncontemplates a strikingly simple, electrically operable remote volumecontrol in which the capacity of the leads connecting the receiver tothe remote point has substantially no effect upon the speechreproduction circuits of the receiver.

If desired, the diode rectifiers 20 and 60 may be replaced by a single,double diode rectifier or detector but in this case some slight capacitycoupling may exist between the remote volume control circuit and thesignal input circuit. However, in actual test, this intercoupling hasbeen found insufficient to exert any substantial effect on the speechreproduction circuits of the receiver. In an actual installation, a BL?tube was employed for the tube 2 and a 61-16 double rectifier tubeemployed for the tubes 20 and 60. The values of the resistances employedwere as follows. 15, l megohm; l8, .5 megohm; 26 150,000 ohms; 32,200,000 ohms, 40, 1 megohm; 64, 1 megohm; 66, 6,000 ohms; and i3, 1rnegohm. The values of the condensers were as follows. I4, I65 and 2B,.02 40 microfarad. The condenser 12 was .1 microfarad; the condenser 14was .5 microfarad and the condenser 16 was of the usual value employedwith a screen grid.

Changes may be made in the form, construc- 45 tion and arrangement ofthe parts without departing from the spirit of the invention orsacrificing any of its attendant advantages, and the right is herebyreserved to make all such changes as fairly fall within the scope of thefollowing 50 claims.

The invention is hereby claimed as follows:

1. In combination, a radio receiver having an audio-amplifier comprisinga thermionic I tube having a plate, a cathode and a pair of control 55grids, a detector for supplying rectifier signal voltages to saidamplifier, means including a volume control means located at thereceiver for connecting the output of said detector between one of saidcontrol grids and said cathode, a 60 source of alternating current atsaid receiver, a

rectifier in said receiver, a resistor in the output circuit of saidrectifier, a filter connecting said output resistor to the other controlgrid of said audio-amplifier tube, a variable resistor at a remotepoint, a fixed resistor connected to said variable resistor, a cableconnecting the radio receiver to said variable resistor, said cablecomprising a wire connecting the source of alternating current to saidvariable resistor and a wire connecting said fixed resistor to the inputof said rectifier whereby said variable resistor controls the biasingvoltage impressed by said rectifier on said other control grid therebyto vary the volume of the signal in the output of said audio-amplifiertube.

2. A volume control for a radio receiver having an amplifier and a powersupply source in the receiver independent of the signal currents flowingthrough the amplifier, said volume control comprising a first impedanceat the receiver and connected to said amplifier to supply biasingvoltages to said amplifier, a second impedance at a point remote fromthe receiver, and means connecting the power supply source in serieswith said second impedance and connecting said first impedance acrosssaid second impedance, said connecting means including manuallyadjustable means at the remote point controlling the flow of currentfrom said source through said second impedance for determining the valueof the biasing voltage impressed by the first impedance on saidamplifier.

3. A volume control for a radio receiver having an audio-amplifierhaving a power supply source in the receiver independent of the currentsflowing through the amplifier, an impedance at the receiver andconnected to said amplifier to supply biasing voltage to said amplifier,a resistor at a point remote from the receiver, a circuit connectingsaid resistor in series with said source, means connecting saidimpedance across the resistor to derive control voltages therefromdetermined by the current flowing through said resistor at the remotepoint and manually adjustable means in said circuit for determining thevalue of the current flowing from the source through said resistor.

4. In combination With a radio receiver having an amplifier and a sourceof alternating current in the receiver, a rectifier in the receiver, animpedance in the receiver, an impedance at a point remote from thereceiver, means connecting the impedances in series with the rectifierand the impedance in the receiver to the input of the amplifier toimpress a direct current biasing voltage on the input of said impedance,voltage control means at a point remote from the receiver, meansconnecting said voltage control means in series with the source ofalternating current and impedance at the remote point, means foradjusting said voltage control means to vary the alternating voltageacross the impedance at the remote point whereby the rectified currentthrough the impedance in the receiver is adjustably controlled to varythe biasing voltage on the input of the amplifier.

5. A volume control for a radio receiver having an amplifier and analternating current power supply source in the receiver, a rectifier inthe receiver, a resistor in the receiver in series with the rectifierand connected to said amplifier to supply a direct current biasingvoltage to said amplifier, a resistor at a point remote from thereceiver, a circuit connecting the remote resistor in series with thealternating current source, a circuit connecting said rectifier and theresistor in the receiver in series across the remote resistor to derivecontrol voltages therefrom determined by the current flowing through theremote resistor, and an adjustable resistor at the remote point inseries with the other resistor at the remote point and the power supplysource for determining the value of the alternating current flowing fromthe source through said other resistor at the remote point.

WILLIAM J. SCI-INELL.

